In general, oil thermal power generation is adapted to generate steam at a high pressure in a boiler using crude oil and/or heavy oil as a fuel for the boiler, to thereby rotate a steam turbine by means of the thus-generated steam, leading to power generation. However, such a system is deteriorated in power generation efficiency. Currently, a high-efficiency large-sized oil-fired boiler is developed, however, it merely exhibits generation efficiency as low as about 40%. Thus, it causes a large part of energy to be outwardly discharged in the form of greenhouse gas without being recovered. In addition, it causes a certain amount of SOx to be present in exhaust gas or flue gas discharged therefrom. Although the exhaust gas is subject to flue gas desulfurization, SOx is partially discharged to an ambient atmosphere, leading to environmental pollution.
Further, a gas turbine combined cycle power generation system is executed which is adapted to drive a gas turbine for power generation using natural gas as a heat source therefor and recover waste heat from high-temperature flue gas or exhaust gas discharged from the gas turbine for production of steam, to thereby drive a steam turbine, leading to power generation. The system comes to notice in the art because it is increased in power generation efficiency, reduced in quantity of CO2 generated per unit power generation and highly reduced in content of SOx and NOx in flue gas. When it uses natural gas as feed gas, it is required to transport it from a gas field to a power generation plant through a pipeline or store LNG and gasify it, followed by combustion of it in the gas turbine. Unfortunately, this leads to an increase in cost of equipment.
In view of the foregoing, a method for producing fuel oil for a gas turbine is proposed as disclosed in Japanese Patent Application Laid-Open Publications Nos. 207179/1994 and 209600/1994. Techniques disclosed in the former Japanese publication are constructed so as to subject low-sulfur crude oil having a salt content adjusted to be 0.5 ppm or less to a separation treatment by atmospheric distillation or vacuum distillation to produce gas turbine fuel oil constituted of a low boiling fraction of 0.05% by weight in sulfur content. Techniques disclosed in the latter Japanese Publication are adapted to heat low-sulfur crude oil using waste heat discharged from a gas turbine and then act hydrogen on the low-sulfur crude oil, to thereby reduce a sulfur and heavy metal content in the crude oil, followed by recovery of crude oil thus refined, which is then used as fuel oil for the gas turbine.
Now, an environmental problem comes to notice in the art. Thus, it is highly required to minimize a content of a sulfur compound in flue gas. This would be solved by employment of a flue gas desulfurization unit. Unfortunately, in power generation using gas turbine fuel oil, arrangement of the flue gas desulfurization unit causes a deterioration in power generation efficiency due to a pressure loss, so that it is required to minimize a sulfur content of gas turbine fuel oil. Thus, the techniques of the former Japanese publication cause the amount of firing of oil to be considerably restricted in the atmospheric distillation or vacuum distillation, to thereby fail to increase the amount of light oil or light distillate to be fed to the gas turbine or the amount of gas turbine fuel oil. This causes yields of gas turbine fuel oil based on crude oil to be as low as a level of 40%, even if Middle East crude oil which has a low sulfur content is used. An increase in firing of oil for the purpose of increasing the yields causes an increase in production of sulfur.
Also, when it is applied to crude oil which is readily available and increased in sulfur content, recovery of light oil or light residue in the same amount causes a sulfur content of the light oil to exceed a specified level, so that it is unsuitable for use as fuel oil for a gas turbine. Thus, it is forced to decrease recovery of the light oil, resulting in application to the crude oil being technically and economically disadvantageous.
The latter Japanese publication discloses techniques of producing hydrogen using methanol as a starting material and subjecting crude oil to hydrotreating with the hydrogen thus produced. However, the techniques are constructed so as to treat crude oil at a low sulfur content, so that application of the techniques to crude oil at a high sulfur content is considerably restricted. Further, the hydrotreating is carried out on crude oil rather than light oil or light distillate obtained by distillation of crude oil, so that it is required to accommodate process conditions to heavy oil or residue contained in crude oil. This requires to increase a reaction temperature, a reaction pressure and reaction time or a period of time during which heavy oil is kept contacted with a catalyst in the reaction. Unfortunately, this causes excessive cracking of light oil in the crude oil, resulting in LPG or the like being contained in a large amount in fuel oil for a gas turbine, so that storage of the fuel oil causes a part thereof to be gasified. This requires to increase pressure resistance of a tank to a significantly high level. Also, the reaction temperature and reaction pressure are caused to be increased, so that a reaction vessel for the hydrotreating is complicated in structure and increased in manufacturing cost. Further, an increase in reaction time requires large-sizing of a catalyst carrier, leading to large-sizing of the reaction vessel and an increase in consumption of a catalyst.